A nano-molar level fluorogenic and oxidation state-selective chromogenic dual reversible chemosensor for multiple targets, Cu2+/S2− and Fe3+/F− ions

Abstract

A pyridine–pyrazole–pyrene-based chemosensor, L, has been developed and fully characterized by all the possible techniques (ESI-MS, NMR, CHN, IR etc.). It has been found that the probe, L, selectively recognizes Cu²⁺ ion and Fe³⁺ ion fluorogenically and chromogenically, respectively, among a wide range of competitive metal ions. It has been demonstrated that the probe is not only metal ion-selective but also oxidation state-selective for Fe³⁺ ions. The metal complexes (Cu and Fe) of the ligand were synthesized and characterized using different spectroscopic techniques and they were also characterised X-ray structurally as well, which confirm the stoichiometry (L : M = 2 : 1). The sensitivities for the fluorogenic sensing of Cu²⁺ ions and chromogenic sensing of Fe³⁺ have been found to be as low as nano molar level detection (69 nM and 27 nM, respectively). Further studies reveal that the Cu^IIL₂ complex can act as a “turn-off” fluorescent chemosensor for S²⁻ ions and Fe^IIIL₂ can act as a reversible “turn-off” colorimetric chemosensor for F⁻ ions over other anions.